Joint prostheses

ABSTRACT

A joint prosthesis comprising at least a first and a second load carrying member, the first load carrying member being substantially more shock absorbing and resilient than the second load carrying member.

[0001] The present invention relates to apparatus and methods for jointprosthesis surgery generally.

[0002] Joint prostheses are well known in the art. Generally jointprostheses include a metal portion, typically constructed of steel ortitanium, which articulates with a bony portion of the body.Non-articulating portions of the prosthesis are generally fixedlyattached to tissue or bone. For example, a hip joint prosthesis of theart generally includes a metallic femoral head which articulates with aportion of the hip bone, and a metallic stem which is fixedly attachedto the femur.

[0003] Several problems are associated with prostheses of the art, forexample, due to the mismatch between material properties of theprosthesis and bone. The contact between metal and bone may causefretting wear of the bone. The difference in coefficient of thermalexpansion between metal and bone may cause discomfort to the patient,especially during weather changes. The metallic prosthesis providesvirtually no shock absorption or damping.

[0004] It is known that a bone grows or regenerates according to thestress which it must bear. The metal prosthesis generally bears a muchlarger portion of weight than the surrounding bone. The reduced stresson the surrounding bone may tend to contribute to degeneration andrecession of the bone, and to create an undesirable gap between the boneand the prosthesis.

[0005] In order to overcome the aforementioned problems, a great varietyof prostheses with resilient portions have been proposed and developed.The following U.S. patents are believed to be representative of the art:U.S. Pat. Nos. 5,522,904, 5,514,184, 5,514,182, 5,507,836, 5,507,833,5,507,830, 5,507,823, 5,507,820, 5,507,818, 5,507,814, 5,491,882,5,489,311, 5,458,651, 5,458,643, 5,448,489, 5,425,779, 5,415,662,5,405,411, 5,405,403, 5,389,107, 5,387,244, 5,376,125, 5,376,064,5,370,699, 5,358,525, 5,344,459, 5,336,268, 5,330,534, 5,326,376,5,316,550, 5,314,494, 5,314,493, 5,314,478, 5,290,314, 5,282,868,5,222,985, 5,217,499, 5,217,498, 5,201,882, 5,201,881, 5,197,989,5,197,987, 5,181,925, 5,171,276, 5,156,631, 5,151,521, 5,147,406,5,146,933, 5,133,763, 5,116,374, 5,108,451, 5,108,446, 5,080,677,5,049,393, 5,041,140, 5,019,107, 5,002,581, 4,997,447, 4,963,154,4,963,153, 4,955,919, 4,955,912, 4,950,298, 4,938,773, 4,938,771,4,936,856, 4,919,678, 4,919,674, 4,908,035, 4,904,269, 4,888,020,4,822,365, 4,813,962, 4.808,186, 4,795,474, 4,795,470, 4,715,859,4,664,668, 4,662,889, 4,661,112, 4,570,270, 4,344,193 and 3,875,594.

[0006] The present invention seeks to provide improved joint prostheseswhich, inter alia, help overcome the above mentioned problems of theprior art.

[0007] The prostheses provide shock absorption, damping and resiliency.Portions of the prostheses which interface with human tissue arepreferably constructed of resilient materials which are compatible withhuman bone or tissue, such as certain types of polyurethane. Certainportions of the prostheses may be constructed of composite materialswhose mechanical or physical properties may be optimized, such as tomatch properties of the local human bone or tissue. By matchingproperties of the local bone or tissue, the prosthesis behavesmechanically, structurally and thermally in a manner similar to thelocal bone or tissue, which helps make the prosthesis more efficient andcomfortable.

[0008] An important feature of the prostheses is that they helpdistribute stresses optimally, thereby stimulating regeneration of bone.

[0009] The present invention is applicable for any joint in which thereis free movement, known in technical terms as a true diarthrosis. Truediarthroses include:

[0010] 1. Gliding joints, known as arthrodias, in which the surfaces ofthe joint are flat, such as in the carpal bones;

[0011] 2. Hinge joints, known as ginglymi, such as the knee or elbow;

[0012] 3. Condyloid joints, known as condylarthroses, which allowflexion, extension and lateral movement, but no rotation, such as thewrist, and saddle-shaped joints which allow the same type of movement ascondyloid joints, but are generally stronger, such as thecarpometacarpal joint of the thumb;

[0013] 4. Ball and socket joints, known as enarthroses, such as the hipand the shoulder; and

[0014] 5. Pivot joints, known as trochoides, which only allow rotation,such as the radio-ulnar joints.

[0015] The present invention will be described in detail hereinbelowwith respect to a prosthesis for an enarthrosis, such as the hip joint,and to a prosthesis for a ginglymus, such as the knee joint. It isappreciated, however, that a prosthesis for any true diarthrosis is inthe scope of the present invention.

[0016] In a radical departure from the prior art, and in accordance withone embodiment of the present invention, a hip joint prosthesis isprovided which includes an artificial femoral head which is not fixedlyattached to the femur, but rather articulates with both the femur andthe acetabulum. The artificial femoral head is generally spherical andmay absorb shocks, provide damping and/or be resilient. A separate,artificial femoral head is easier to insert than the prostheses of theprior art which have a stem.

[0017] In addition, the artificial femoral head may be provided withdelimiting rails or grooves which serve to define and limit the movementpaths of the femur with respect to the body, if required, anddislocation of the joint is substantially prevented. The delimitingrails or grooves may also serve as bumpers which damp and cushion thefemoral head at the limits of its articulation.

[0018] The prostheses of the present invention may also be provided withpassageways for fluid, such as synovial fluid. Fluid present in thesepassageways helps to lubricate the prosthesis and provides viscousdamping.

[0019] Since the prostheses of the present invention are resilient, theygeometrically adapt themselves to changes in static and dynamic forcesborne by the joint. In the case of the hip joint prosthesis of thepresent invention, for example, normal raising of the thigh does notapply substantial forces on the hip joint, and the resilient hip jointprosthesis allows the freedom of movement of a ball and socket jointwith substantially no deformation nor obstruction to movement due tofriction between the prosthesis and human tissue or bone, or betweenadjacent regions of the prosthesis, such as between the artificialfemoral head and an artificial socket.

[0020] In contrast, when the person is standing, the static force of theweight of the person on the hip joint causes the resilient prosthesis todeform somewhat, i.e., to be squashed a certain amount. This deformationprovides a relatively larger area for supporting the weight on thejoint, thereby reducing pressure on the joint. The deformation alsoincreases the friction force between the prosthesis and human tissue orbone, or between adjacent regions of the prosthesis, such as between theartificial femoral head and an artificial socket. The increased frictionis beneficial because it does not hinder the stationary person; on thecontrary, the increased friction increases stability of the person.

[0021] The resiliency of the prosthesis is also beneficial during suddenslips or falls. The dynamic and/or static forces due to the suddenmovement tend to deform or squash the resilient prosthesis. As describedabove, the deformation reduces pressure on the joint, reduces danger ofthe prosthesis detaching from the bone, and increases friction whichhelps provide stability during the slip or fall.

[0022] There is thus provided in accordance with a preferred embodimentof the present invention, a joint prosthesis including at least a firstand a second load carrying member, the first load carrying member beingsubstantially more shock absorbing and resilient than the second loadcarrying member.

[0023] In accordance with a preferred embodiment of the presentinvention, at least one of the load carrying members is characterized inhaving at least one of strength and elasticity generally similar to thatof human cartilage.

[0024] There is also provided in accordance with a preferred embodimentof the present invention, a joint prosthesis including a plurality ofalternating adjacent portions of substantially rigid and substantiallyresilient materials.

[0025] There is also provided in accordance with a preferred embodimentof the present invention, a joint prosthesis including a plurality ofalternating adjacent first and second portions, the first portion havinga substantially rigid configuration and the second portion having asubstantially resilient configuration.

[0026] Preferably at least one of the first and the second portions isgenerally omega shaped. The joint prosthesis may include at least oneportion compatible with human tissue. The joint prosthesis may have atleast one hollow portion.

[0027] Preferably, any of the joint prostheses includes at least onedelimiting rail or groove.

[0028] Preferably, any of the joint prostheses includes at least onepassageway for a fluid.

[0029] There is also provided in accordance with a preferred embodimentof the present invention, a hip joint prosthesis including anartificial, spherical femoral head which is adapted to articulate withan acetabulum and an upper portion of a thigh.

[0030] There is also provided in accordance with a preferred embodimentof the present invention, a hip joint prosthesis including anartificial, self-articulating femoral head, the head being attachable toat least one of an acetabulum and an upper portion of a thigh.

[0031] Preferably, the hip joint prosthesis includes an artificialfemoral head which is shock absorbing, provides damping and/or issubstantially resilient.

[0032] Preferably, the femoral head has at least one hollow portion.

[0033] Further in accordance with a preferred embodiment of the presentinvention, the hip joint prosthesis also includes an artificialacetabulum attachable to an innominate bone, the artificial femoral headarticulating with the artificial acetabulum.

[0034] Still further in accordance with a preferred embodiment of thepresent invention, the hip joint prosthesis also includes an artificialfemoral socket attachable to a femur, the artificial femoral headarticulating with the artificial femoral socket.

[0035] Further in accordance with a preferred embodiment of the presentinvention, the artificial femoral head includes a device forsubstantially preventing dislocation of the artificial femoral head fromthe artificial acetabulum, the artificial femoral socket, or both.

[0036] Preferably the device for substantially preventing dislocation isshock absorbing or resilient.

[0037] Further in accordance with a preferred embodiment of the presentinvention, the artificial femoral head includes at least one delimitingrail or groove. The delimiting groove may have a different geometricalshape than that of the rail. This permits providing variouspredetermined ranges and paths of motion.

[0038] Still further in accordance with a preferred embodiment of thepresent invention, the artificial femoral head has at least onepassageway for a fluid.

[0039] Additionally in accordance with a preferred embodiment of thepresent invention, the hip joint prosthesis includes a sleeve whichenvelops at least one portion of the prosthesis and which is attachableto at least one of a portion of an innominate bone and a thigh.Preferably the sleeve includes a relatively high strength fabric.

[0040] Further in accordance with a preferred embodiment of the presentinvention, the artificial femoral socket is adapted to fit substantiallysnugly with at least one upper portion of a femur.

[0041] Still further in accordance with a preferred embodiment of thepresent invention, the artificial femoral head includes a plurality ofalternating adjacent portions of substantially rigid and substantiallyresilient materials.

[0042] Additionally in accordance with a preferred embodiment of thepresent invention, the hip joint prosthesis further includes a steminsertable into a femur.

[0043] Further in accordance with a preferred embodiment of the presentinvention, the hip joint prosthesis includes an outer layer attachableto a femur, the outer layer including a material compatible with humantissue.

[0044] There is also provided in accordance with a preferred embodimentof the present invention, a knee joint prosthesis including a femoralportion and a tibial portion, the femoral portion being attachable to afemur and the tibial portion being attachable to a tibia, the femoralportion articulating with the tibial portion, wherein at least one ofthe femoral portion and the tibial portion is shock absorbing, providesdamping or is substantially resilient.

[0045] In accordance with a preferred embodiment of the presentinvention, the knee joint prosthesis includes a device operative tolimit motion of the tibia with respect to the femur.

[0046] Preferably, the device operative to limit motion of the tibiawith respect to the femur, is shock absorbing.

[0047] Additionally in accordance with a preferred embodiment of thepresent invention, the femoral portion is generally convex and thetibial portion is generally concave.

[0048] Alternatively in accordance with a preferred embodiment of thepresent invention, the femoral portion is generally convex and thetibial portion is generally convex.

[0049] Further in accordance with a preferred embodiment of the presentinvention, the knee joint prosthesis includes at least one rollerelement, the femoral portion articulating with the tibial portion viathe at least one roller element.

[0050] Preferably, the knee joint prosthesis has at least one fluidpassageway.

[0051] There is also provided in accordance with a preferred embodimentof the present invention, a bone fastener including a plurality ofalternating adjacent portions of substantially rigid and substantiallyresilient materials.

[0052] There is also provided in accordance with a preferred embodimentof the present invention, a bone fastener, including a plurality ofalternating adjacent first and second portions, the first portion havinga substantially rigid configuration and the second portion having asubstantially resilient configuration.

[0053] There is also provided in accordance with a preferred embodimentof the present invention, a method of incision of a ligament includingforming a substantially wave-like incision in the ligament.

[0054] There is also provided in accordance with a preferred embodimentof the present invention, a method of insertion of a hip jointprosthesis including:

[0055] fixedly attaching a first joint element to an upper portion of afemur, the first joint element fitting substantially snugly with theupper portion of the femur;

[0056] fixedly attaching a second joint element to a portion of aninnominate bone; and

[0057] inserting an artificial femoral head intermediate the first andthe second joint elements, such that the artificial femoral headarticulates with at least one of the first and the second jointelements.

[0058] Preferably, one or more natural or artificial ligaments may beused to strengthen the hip joint.

[0059] There is also provided in accordance with a preferred embodimentof the present invention, a method for limiting a range of movement of ahip joint including:

[0060] implanting a hip joint prosthesis comprising at least onedelimiting rail and at least one delimiting groove, the at least onedelimiting rail articulating with the at least one delimiting groove,such that the at least one delimiting groove limits articulation of theat least one delimiting rail therein.

[0061] The present invention will be understood and appreciated from thefollowing detailed description, taken in conjunction with the drawingsin which:

[0062]FIG. 1 is a simplified illustration of a human hip joint;

[0063]FIG. 2 is a simplified illustration of a hip joint prosthesis,constructed and operative in accordance with a preferred embodiment ofthe present invention;

[0064]FIG. 3 is a partially sectional illustration of the hip jointprosthesis of FIG. 2;

[0065]FIG. 4 is a partially sectional illustration of the hip jointprosthesis of FIG. 2, wherein the femur is rotated laterally;

[0066]FIG. 5 is a partially sectional illustration of the hip jointprosthesis of FIG. 2, wherein the femur is rotated rearwardly;

[0067]FIG. 6 is a simplified pictorial illustration of an artificialfemoral head of the hip joint prosthesis of FIG. 2, the femoral headcomprising two delimiting rails;

[0068]FIGS. 7A and 7B are simplified illustrations of an artificialfemoral head, constructed and operative in accordance with anotherpreferred embodiment of the present invention, articulating withartificial and natural acetabula respectively, and wherein theartificial femoral head has no delimiting rails;

[0069]FIGS. 8A and 8B are simplified illustrations of an artificialfemoral head fixedly attached to a stem, constructed and operative inaccordance with yet another preferred embodiment of the presentinvention, articulating with artificial and natural acetabularespectively, and wherein the artificial femoral head has no delimitingrails;

[0070]FIG. 8C is a simplified illustration of an artificial,self-articulating femoral head fixedly attached to a stem and to anacetabulum, constructed and operative in accordance with a preferredembodiment of the present invention;

[0071]FIG. 9A is a simplified pictorial illustration of an artificialfemoral head and an artificial acetabulum, constructed and operative inaccordance with still another preferred embodiment of the presentinvention, and wherein the artificial femoral head has one delimitingrail which articulates with the generally elliptically shapedacetabulum;

[0072]FIG. 9B is a simplified sectional illustration of the femoral headof FIG. 9A, taken along lines 9B-9B in FIG. 9A;

[0073]FIG. 9C is a simplified pictorial illustration of a flexible andstable bone connector, constructed and operative in accordance with apreferred embodiment of the present invention;

[0074]FIGS. 9D and 9E are simplified, sectional illustrations of aflexible and stable bone connector stem of a hip joint prosthesis,constructed and operative in accordance with a preferred embodiment ofthe present invention, before and after deployment, respectively;

[0075]FIGS. 9F and 9G are simplified, sectional illustrations of aflexible and stable bone connector stem of a hip joint prosthesis,constructed and operative in accordance with another preferredembodiment of the present invention, before and after deployment,respectively;

[0076]FIG. 10 is a simplified sectional illustration of a non-hollowartificial femoral head, constructed and operative in accordance with apreferred embodiment of the present invention;

[0077]FIG. 11 is a simplified sectional illustration of an artificialfemoral head, constructed and operative in accordance with anotherpreferred embodiment of the present invention, and wherein the femoralhead comprises a plurality of hollow portions;

[0078]FIG. 12 is a simplified sectional illustration of an artificialfemoral head, constructed and operative in accordance with yet anotherpreferred embodiment of the present invention, and wherein the femoralhead comprises a plurality of hollow portions filled with a fluid;

[0079]FIG. 13 is a simplified sectional illustration of an artificialfemoral head, constructed and operative in accordance with still anotherpreferred embodiment of the present invention, and wherein the femoralhead comprises a plurality of portions, each portion not necessarilyhaving the same mechanical or physical properties;

[0080]FIG. 14A is a simplified sectional illustration of an artificialfemoral head, constructed and operative in accordance with anotherpreferred embodiment of the present invention, and wherein the femoralhead comprises a protruding delimiting bumper;

[0081]FIG. 14B is a simplified sectional illustration of an artificialfemoral head, constructed and operative in accordance with yet anotherpreferred embodiment of the present invention, and wherein the femoralhead comprises a thin, resilient outer shell and a resilient core;

[0082]FIG. 15 is a simplified pictorial illustration of an artificialfemoral head, constructed and operative in accordance with a preferredembodiment of the present invention, and including delimiting grooves;

[0083]FIG. 16 is a simplified sectional illustration of an artificialfemoral head, constructed and operative in accordance with anotherpreferred embodiment of the present invention, and wherein the femoralhead has fluid passageways;

[0084]FIG. 17 is a simplified sectional illustration of an artificialfemoral head, constructed and operative in accordance with yet anotherpreferred embodiment of the present invention;

[0085]FIGS. 18A and 18B are simplified pictorial and sectionalillustrations respectively of an artificial femoral head, constructedand operative in accordance with another preferred embodiment of thepresent invention, and wherein the femoral head comprises a plurality ofalternating adjacent portions of substantially rigid and substantiallyresilient materials, FIG. 18B being taken along lines 18B-18B in FIG.18A;

[0086] FIGS. 18C-18F are simplified pictorial illustrations ofalternative constructions of a femoral head including a plurality ofalternating adjacent portions of substantially rigid and substantiallyresilient materials;

[0087]FIG. 18G is a simplified pictorial illustration of an artificialacetabulum, constructed and operative in accordance with a preferredembodiment of the present invention;

[0088]FIGS. 18H, 18I and 18J are simplified illustrations of installingthe artificial acetabulum of FIG. 18G into a natural acetabulum, inaccordance with a preferred embodiment of the present invention;

[0089]FIGS. 18K and 18L are simplified sectional illustrations of twoartificial acetabula, constructed and operative in accordance with twopreferred embodiments of the present invention;

[0090] FIGS. 19A-19C are simplified pictorial illustrations of a methodof incision of ligaments, such as prior to insertion of a hip jointprosthesis, in accordance with a preferred embodiment of the presentinvention;

[0091]FIG. 20 is a simplified pictorial illustration of a sleeve forjoining a femoral head with the innominate bone, constructed andoperative in accordance with a preferred embodiment of the presentinvention;

[0092]FIG. 21 is a simplified sectional illustration of an expandableartificial femoral head, constructed and operative in accordance with apreferred embodiment of the present invention;

[0093]FIG. 22 is a simplified illustration of a human knee joint;

[0094]FIGS. 23 and 24 are respective simplified side and front viewillustrations of a knee joint prosthesis, constructed and operative inaccordance with a preferred embodiment of the present invention;

[0095]FIG. 25 is a simplified illustration of a femoral portion of theknee joint prosthesis of FIGS. 23 and 24;

[0096]FIG. 26 is a simplified illustration of a tibial portion of theknee joint prosthesis of FIGS. 23 and 24;

[0097]FIGS. 27 and 28 are respective simplified side and front viewillustrations of a knee joint prosthesis, constructed and operative inaccordance with another preferred embodiment of the present invention;

[0098]FIGS. 29 and 30 are respective simplified side and front viewillustrations of a knee joint prosthesis, constructed and operative inaccordance with yet another preferred embodiment of the presentinvention;

[0099]FIGS. 31 and 32 are respective simplified side and front viewillustrations of a knee joint prosthesis, constructed and operative inaccordance with still another preferred embodiment of the presentinvention;

[0100]FIG. 33 is a simplified illustration of a roller element includedin the knee joint prosthesis of FIGS. 31 and 32;

[0101]FIG. 34 is a simplified, partially sectional illustration of abone fastener, constructed and operative in accordance with a preferredembodiment of the present invention; and

[0102]FIG. 35 is a simplified, partially sectional illustration of avertebra replacement, constructed and operative in accordance with apreferred embodiment of the present invention.

[0103] The present invention will now be described in detail withrespect to a prosthesis for an enarthrosis, an example being the hipjoint, and to a prosthesis for a ginglymus, an example being the kneejoint. It is appreciated, however, that a prosthesis for any truediarthrosis is in the scope of the present invention.

[0104] For a better understanding of a hip joint prosthesis, a basicdescription of the human hip joint is presented here with reference toFIG. 1, which illustrates the hip of the right side of the body. The hipjoint is a ball and socket joint, the ball being the femoral head (headof the thigh bone) which articulates with the acetabulum of theinnominate bone, known in non-technical terms as the socket of the hipbone.

[0105] The innominate bone in the area of the hip joint is made of threeportions: the upper portion is called the ilium, the middle portion iscalled the pubis and the lower portion is called the ischium. Thefemoral head is connected to the innominate bone by a plurality ofligaments. The ligaments shown in FIG. 1 are the iliofemoral ligamentsand the pubo-femoral ligament. There is also an ischio-femoral ligament,not seen in FIG. 1. The femoral head articulates with a fibrous rim ofthe acetabulum called the cotyloid ligament.

[0106] Generally a hip joint replacement of the prior art involvesreplacing the natural femoral head with a metallic artificial femoralhead which is fixedly attached to a stem. The stem is generally insertedin the femur and the femoral head articulates with the acetabulum, ifstill intact, or some other depression, artificial or natural, in theinnominate bone. Some or all of the ilio-femoral, pubo-femoral andischio-femoral ligaments may be removed to provide access to the femoralhead and acetabulum.

[0107] Reference is now made to FIGS. 2 and 3 which illustrate a hipjoint prosthesis 10, constructed and operative in accordance with apreferred embodiment of the present invention. In a radical departurefrom the prior art, hip joint prosthesis 10 comprises a femoral head 12which is not fixedly attached to the femur, but rather is capable ofarticulating with both the thigh and the innominate bone. In accordancewith a preferred embodiment of the present invention, femoral head 12may be constructed of a rigid material compatible with human tissue, forexample, a metal such as stainless steel, or a structural plastic.

[0108] In accordance with another preferred embodiment of the presentinvention, artificial femoral head 12 is constructed of a material whichis shock absorbing, and additionally or alternatively provides damping,and additionally or alternatively is resilient. An example of such amaterial is polyurethane or synthetic rubber.

[0109] A resilient artificial femoral head, unlike the prior art, yieldsupon application of forces and substantially returns to its originalshape after such forces are removed.

[0110] Artificial femoral head 12 is preferably, although notnecessarily, generally spherical in shape. In accordance with apreferred embodiment of the present invention, and as shown in FIG. 3,femoral head 12 has a hollow core 14. Hollow core 14, inter alia, addsto the resiliency and shock absorbing characteristics of femoral head12.

[0111] In accordance with a preferred embodiment of the presentinvention, hip joint prosthesis 10 also comprises an artificialacetabulum 16 which is preferably fixedly attached to the innominatebone via an acetabulum interface 18. Artificial femoral head 12articulates with artificial acetabulum 16.

[0112] Additionally in accordance with a preferred embodiment of thepresent invention, hip joint prosthesis 10 comprises an artificialfemoral socket 20 which is preferably fixedly attached to the femur viaa stem 22. Alternatively, socket 20 may be attached to the femur withouta stem, for example, by bonding. Artificial femoral head 12 articulateswith artificial femoral socket 20. Socket 20 is shaped to facilitatethis articulation, such as being generally concave. In addition, socket20 is preferably shaped to overlap, or snugly fit, the upper portion ofthe natural femur. The generally concave, overlapping shape ofartificial femoral socket 20 helps distribute stresses optimally on thefemur, thereby stimulating regeneration of bone.

[0113] Socket 20 may overlap and “hug” the upper portion of the femur onthe outside surface of the femur. Alternatively or additionally, socket20 may be configured to fit snugly into an inner surface of the femur.

[0114] It is important to note that socket 20 serves two general tasks,as described above. The first task is articulation with artificialfemoral head 12. The second task is fitting snugly with the femur anddistributing stresses evenly thereon.

[0115] It is appreciated that in accordance with another preferredembodiment of the present invention, socket 20 may comprise two separateportions each generally dedicated to serving one of the above describedtasks. A first portion 20A, generally concave in shape, may be generallydedicated to articulation with artificial femoral head 12. A secondportion 20B, generally shaped as a “crown” to hug and snugly fitcircumferentially around and on top of the femur, may be generallydedicated to distributing stresses evenly on the femur. This is true ofany of the sockets described herein with reference to any of theembodiments of the present invention. The “crown”, i.e., second portion20B, greatly changes the loading conditions of prosthesis 10, decreasesstresses exerted on the femur by stem 22, and creates a new andhealthier stress distribution on the surrounding bone and tissue. Withthe support of second portion 20B, stem 22 may have a much smallersection throughout and particularly at its neck.

[0116] Stem 22 preferably includes a core 24 and an outer layer 26, asseen in FIGS. 2 and 3. Outer layer 26 preferably includes one or moreridges 28, which, inter alia, help distribute stresses and help fastenstem 22 to the femur.

[0117] Core 24 of stem 22, artificial acetabulum 16 and artificialfemoral socket 20 are preferably constructed of a rigid material, forexample, stainless steel or a structural plastic. Alternatively, therigid material may be a composite material, such as a lay-up of graphitefibers, which may be constructed to have mechanical or physicalproperties, such as modulus of elasticity or coefficient of thermalexpansion, equivalent to that of the local human bone.

[0118] Stem 22 provides excellent three-dimensional anchorage to thebone, and induces three-dimensional loading stress conditions as closeas possible to the natural conditions. The improved stress fielddistribution at the interface between the prosthesis and the bone helpsprevent lysis. The stress field set up by the prosthesis inside the bonehelps induce regeneration and strengthening of the bone.

[0119] Acetabulum interface 18 and outer layer 26 of stem 22 arepreferably made of a resilient material compatible with human tissue,such as polyurethane, which helps distribute stresses optimally, therebystimulating regeneration of bone. In accordance with a preferredembodiment of the present-invention, acetabulum interface 18 and outerlayer 26 of stem 22 are constructed of a material, such as polyurethane,which has one or more mechanical and/or physical propertiessubstantially similar to human cartilage.

[0120] Hip joint prosthesis 10 may include a device for facilitatingremoval as is known in the art, such as a threaded boss or hole (bothnot shown).

[0121] It may sometimes be desired to limit the number of degrees offreedom of the hip joint or the range of a particular degree of freedomof movement of the femur with respect to the acetabulum, depending onthe needs of the patient. It may also be desired to provide safeguardsto substantially prevent dislocation of the joint. In accordance with apreferred embodiment of the present invention, apparatus is provided toachieve these goals, as is now described.

[0122] Reference is now made additionally to FIGS. 4-6. In accordancewith a preferred embodiment of the present invention, artificial femoralhead 12 is provided with an upper delimiting rail 30 and a lowerdelimiting rail 32. Upper delimiting rail 30 slides in a channel 34 inartificial acetabulum 16. Channel 34 is oriented generally forwards andrearwards with respect to the human body. As seen in FIG. 5, upperdelimiting rail 30 slides forwards in channel 34 when the femur is movedbackwards. It is appreciated that upper delimiting rail 30 slidesbackwards in channel 34 when the femur is moved forwards.

[0123] Lower rail 32 slides in a channel 36 in artificial femoral socket20. As seen in FIG. 4, as the femur is moved laterally away from thebody, lower rail 32 slides in channel 36 of socket 20 and buttsthereagainst. Upper delimiting rail 30 is similarly constrained to slidein channel 34. Constraining the travel of rails 30 and 32 in channels 34and 36, respectively, substantially prevents overtravel of the femur andsubstantially prevents dislocation of artificial femoral head 12 fromartificial acetabulum 16 and artificial femoral socket 20. Moreover,since femoral head 12 is preferably constructed of a shock absorbing orresilient material, the butting of rails 30 and 32 against channels 34and 36, respectively, is substantially cushioned and damped.

[0124] Variations of hip joint prosthesis 10 are possible within thescope of the present invention. Reference is now made to FIGS. 7A and 7Bwhich illustrate an artificial femoral head 40, constructed andoperative in accordance with another preferred embodiment of the presentinvention. Artificial femoral head 40 may be similar in construction andoperation to artificial femoral head 12 of FIGS. 2-6. Femoral head 40differs from femoral head 12 in that femoral head 40 has no delimitingrails. In FIG. 7A, femoral head 40 is shown articulating with anartificial acetabulum 42. In FIG. 7B, femoral head 40 is shownarticulating with a natural acetabulum 44.

[0125] Reference is now made to FIGS. 8A and 8B which illustrate anartificial femoral head 46 fixedly attached to a crown 48, constructedand operative in accordance with yet another preferred embodiment of thepresent invention. Femoral head 46 and crown 48 may be constructed of aresilient material, such as polyurethane.

[0126] Crown 48 may be attached to an upper portion of the thigh.Alternatively, as shown in FIG. 8A, crown 48 may be attached to a stem49. Stem 49 may include a core 49A and an outer layer 49B. Core 49A maybe of solid construction, and additionally or alternatively, may includeat least one hollow portion. Outer layer 49B may be constructed of amaterial with properties similar to human cartilage.

[0127] In FIG. 8A, femoral head 46 articulates with an artificialacetabulum 50. Femoral head 46 may have an upper delimiting rail (notshown) which articulates with a corresponding groove (not shown) inartificial acetabulum 50. Alternatively, femoral head 46 may have adelimiting groove with which articulates a corresponding rail inartificial acetabulum 50.

[0128] In FIG. 8B, femoral head 46 articulates with a natural acetabulum52. Femoral head 46 may include a hollow portion (not shown), asdescribed hereinabove for artificial femoral head 12 with respect toFIGS. 2-6.

[0129] Alternatively, in accordance with another preferred embodiment ofthe present invention, artificial femoral head 46 may be fixedlyattached to artificial acetabulum 50. In such an embodiment, artificialfemoral head 46 may articulate with crown 48.

[0130] Reference is now made to FIG. 8C which illustrates an artificial,self-articulating femoral head 55 fixedly attached to a stem 56 and toan artificial acetabulum 57, constructed and operative in accordancewith a preferred embodiment of the present invention. Femoral head 55 ispreferably constructed of a resilient material, such as polyurethane.Artificial acetabulum 57 may have any suitable shape, typically beinggenerally shell-shaped or spherical.

[0131] Articulation of the thigh with the innominate bone is notachieved by articulation of femoral head 55 with artificial acetabulum57, but rather is achieved by the self-articulation of femoral head 55.“Self-articulation” is defined as the ability of femoral head 55 topermit rotary and translatory motion of the thigh with respect to theinnominate bone due to the resilient and elastic properties andconfiguration of femoral head 55. Stem 56 may comprise an outer layer 58which may have properties similar to human cartilage.

[0132] Reference is now made to FIGS. 9A and 9B which illustrate anartificial femoral head 60 and an artificial acetabulum 62, constructedand operative in accordance with still another preferred embodiment ofthe present invention. Artificial femoral head 60 has one delimitingrail 64 which articulates with a generally elliptically shaped recess 66in artificial acetabulum 62. It is appreciated that this type of railmay be employed in any of the other artificial femoral heads describedherein, either as an upper rail or a lower rail or both.

[0133] Artificial femoral head 60 may be provided with one or more fluidpassageways 67, as seen in FIG. 9A, for flow therethrough of a fluid(not shown), such as synovial fluid. It is appreciated that any of theartificial femoral heads of the present invention may be provided withfluid passageways. Fluid passageways 67 help lubricate artificialfemoral head 60, and provide damping.

[0134] Reference is now made to FIG. 9C which illustrates a flexible andstable bone connector 450, constructed and operative in accordance witha preferred embodiment of the present invention. Connector 450preferably includes a hollow, generally tubular portion 452 and a boneinterface portion 454. Interface portion 454 is preferably shaped tosnugly fit the inner geometry of the bone into which it is placed. Theinner geometry of the bone may be determined by such methods as acomputer tomography, and interface portion 454 may then be machinedaccordingly.

[0135] In accordance with a preferred embodiment of the presentinvention, interface portion 454 has a fluted shape with a plurality ofprotruding fins 456. The fluted shape of interface portion 454 and thehollowness of tubular portion 452 promote bone development and growthafter implanting the prosthesis. Connector 450 may be fashioned in avariety of configurations, such as straight, curved, cylindrical ortapered, for example.

[0136] A known problem associated with the repair of broken bones andwith the insertion of stems of femoral prostheses into femurs, is thatthe bone may have a curvature which changes along the length thereof inthree dimensions. It is difficult to match the curvature of the stem ofthe prosthesis to the natural curvature of the bone. In practice,usually a set of standardized connecting pins or prostheses are used andthe closest matching prosthesis is selected and further machined orfiled in the operating theater to match the measured natural curvatureof the femur. Even with this method, gaps are almost inevitable betweenthe prosthesis and the inner bone tissue.

[0137] It is a particular feature of the present invention thatconnector 450 is sufficiently flexible so that it can be inserted into abored portion of the bone, such as a femur, and deform to adapt to thechanging curvature of the bone, thereby helping to solve theaforementioned problem. Connector 450 is preferably constructed of amaterial which provides flexibility to permit insertion into the bone,while at the same time providing sufficient structural stability onceconnector 450 is in place. A suitable material is one having anon-linear, “half-bell-shaped” stress-strain relationship, for example,a plastic such as polyurethane. The material may be reinforced withfibers, whose density and orientation may be selected in accordance witha particular engineering requirement.

[0138] Reference is now made to FIGS. 9D and 9E which illustrate aflexible and stable bone connector stem 460 of a hip joint prosthesis,constructed and operative in accordance with a preferred embodiment ofthe present invention. Stem 460 may be readily employed in any of thefemoral prostheses of the present invention.

[0139] Stem 460 is preferably constructed similarly to connector 450,and preferably includes a fluted elongated portion 462 having a hollowportion 464 and a plurality of protruding fins 466. A force transferelement 468, such as a wire, rod or cable, with a plurality of bulges470 is preferably disposed in hollow portion 464. Element 468 may bemade of any suitable stiff, biocompatible material, such as DYNEEMA.

[0140] Stem 460 is preferably inserted into the femur in the orientationshown in FIG. 9D. After insertion, element 468 is then moved generallyin the direction of an arrow 472, thereby causing bulges 470 to deformfluted portion 462, as seen in FIG. 9D, and fix stem 460 firmly in thefemur.

[0141] Reference is now made to FIGS. 9F and 9G which illustrate aflexible and stable bone connector stem 480 of a hip joint prosthesis,constructed and operative in accordance with another preferredembodiment of the present invention. Stem 480 may also be readilyemployed in any of the femoral prostheses of the present invention.

[0142] Stem 480 preferably includes a fluted elongated portion 482 inwhich is disposed a sleeve 484 having a plurality of bulges 486.Disposed inside sleeve 484 is hollow shaft 488. Sleeve 484 is arrangedfor sliding, axial motion with respect to fluted portion 482 and shaft488.

[0143] As describe hereinabove for fluted portion 462, fluted portion482 is sufficiently flexible so that it can be inserted into a boredportion of a femur and deform to adapt to the changing curvature of thefemur.

[0144] Stem 480 is preferably inserted into the femur in the orientationshown in FIG. 9F. After insertion, sleeve 484 is then moved generally inthe direction of an arrow 490, thereby causing bulges 486 to deformfluted portion 482, as seen in FIG. 9D, and fix stem 480 firmly in thefemur.

[0145] Artificial femoral head 12 shown in FIGS. 2-6, has a hollow core14. Reference is now made to FIG. 10 which illustrates a non-hollowartificial femoral head 70, constructed and operative in accordance witha preferred embodiment of the present invention. Artificial femoral head70 may include an upper rail 72 and a lower rail 74.

[0146] Reference is now made to FIG. 11 which illustrates an artificialfemoral head 80, constructed and operative in accordance with anotherpreferred embodiment of the present invention. Femoral head 80 comprisesa plurality of hollow portions 82.

[0147] Reference is now made to FIG. 12 which illustrates an artificialfemoral head 90, constructed and operative in accordance with yetanother preferred embodiment of the present invention. Femoral head 90comprises a plurality of hollow portions 92 filled with a fluid, such assynovial fluid. Additionally or alternatively, one or more fluidpassageways 94 may be provided. The fluid in portions 92 or passageways94 may enhance the shock absorbing and damping characteristics offemoral head 90.

[0148] Reference is now made to FIG. 13 which illustrates an artificialfemoral head 100, constructed and operative in accordance with stillanother preferred embodiment of the present invention. Femoral head 100comprises a plurality of portions 102, each portion 102 not necessarilyhaving the same mechanical or physical properties. Portions 102 may beused to enhance, to optimize or to customize the shock absorbing anddamping characteristics of femoral head 100.

[0149] Reference is now made to FIG. 14A which illustrates an artificialfemoral head 110, constructed and operative in accordance with anotherpreferred embodiment of the present invention. Femoral head 110comprises a protruding delimiting bumper 112 instead of a delimitingrail.

[0150] Reference is now made to FIG. 14B which illustrates an artificialfemoral head 113, constructed and operative in accordance with yetanother preferred embodiment of the present invention. Femoral head 113comprises a thin, resilient outer shell 114 and a resilient core 115.Shell 114 may be constructed of DYNEEMA high performance polyethylenefibers, commercially available from DSM, Netherlands. DYNEEMA,particularly in the form of a woven fabric, provides a combination ofhigh strength with excellent shock absorbing and dampingcharacteristics, as well as being biocompatible. Core 115 may also bemade of DYNEEMA with properties engineered to meet requirements such asstrength or resilience, for example, and may be impregnated with othermaterials, such as a resin.

[0151] Reference is now made to FIG. 15 which illustrates an artificialfemoral head 120, constructed and operative in accordance with apreferred embodiment of the present invention. Femoral head 120 includesdelimiting grooves 122 which articulate with corresponding rails (notshown) in an artificial acetabulum and an artificial socket (not shown).

[0152] Reference is now made to FIG. 16 which illustrates an artificialfemoral head 130, constructed and operative in accordance with anotherpreferred embodiment of the present invention. Femoral head 130 hasfluid passageways 132 which allow flow therethrough of a fluid,preferably synovial fluid, the natural lubrication fluid of the humanbody. Fluid passageways 132 may be configured in a variety oforientations, configurations and sizes. Alternatively or additionally,passageways 132 may be provided in an artificial femoral socket 134 oran artificial acetabulum 136.

[0153] Fluid flowing in fluid passageways 132 may help lubricate femoralhead 130. The presence of fluid in fluid passageways 132 may alsoenhance the shock absorbing and damping characteristics of femoral head130.

[0154] As mentioned above, the ligaments connecting the femur and theinnominate bone may be removed in the prior art, before placement of ahip joint prosthesis. This is unfortunate because these ligaments areamongst the strongest ligaments in the body. These ligaments strengthenthe joint and help prevent dislocation. Preserving some or all of theligaments is therefore desirable.

[0155] Reference is now made to FIG. 17 which illustrates an artificialfemoral head 140, constructed and operative in accordance with yetanother preferred embodiment of the present invention. Artificialfemoral head 140 is preferably relatively small in size, thereby helpingto reduce the need for tampering with some of the hip joint ligaments.In this embodiment, femoral head 140 articulates with an artificialacetabulum 142 and an artificial socket 144. Socket 144 may be attacheddirectly to the femur without a stem, such as by bonding or via a crown(not shown) similar to the crown-shaped portion 20B describedhereinabove with reference to FIGS. 2 and 3.

[0156] By eliminating the stem, the need for tampering with or drillinginto the femur may also be eliminated. There may be no need to removethe entire natural femoral head, but rather a portion thereof may bepreserved. Preserving part of the femur may simplify the surgicaloperation and may preserve most of the strength of the bone.

[0157] The need for tampering with some of the ligaments may also bereduced. Indeed, the intact ligaments themselves act together with theprosthesis of FIG. 17, because they tend to keep femoral head 140properly installed. In addition, the embodiment of FIG. 17 may be moreeasily and quickly implanted than prostheses having stems.

[0158] Other embodiments of the present invention which address theproblem of preserving the hip joint ligaments are described hereinbelowwith respect to FIGS. 19A-21.

[0159] Reference is now made to FIGS. 18A and 18B which illustrate anartificial femoral head 150, constructed and operative in accordancewith another preferred embodiment of the present invention. Femoral head150 comprises a plurality of alternating adjacent portions 152 and 154of substantially rigid and substantially resilient materialsrespectively. The rigid material is preferably a composite material andthe resilient material is preferably polyurethane. In accordance with apreferred embodiment of the present invention, femoral head 150 isattached to an artificial acetabulum 156.

[0160] The material composition and the geometry of the portions 152 and154 may be optimized to provide the desired rigidity and resiliency. Inthis manner, femoral head 150 may be constructed as a non-linear springwith multiple spring constants.

[0161] Femoral head 150 may have different rigidity and resiliency forforward-backward motion as opposed to lateral motion. For example, asseen in FIG. 18B, adjacent portions 152 and 154 are generallyomega-shaped. Such a shape permits relatively easy swinging of the femurforwards and backwards with respect to the body, while at the same timeconstraining the swinging range to prevent overtravel of the femur. Theresiliency of femoral head 150 damps the motion of the femur at thelimits of its swing. The omega shape is stiffer in the lateraldirection, thus limiting lateral motion of the femur with respect to thebody. It is appreciated that femoral head 150 may be alternativelyconstructed to allow greater freedom of motion laterally than forwardsand backwards.

[0162] Reference is now made to FIGS. 18C and 18D which show femoralheads 160 and 162 respectively, with adjacent layers 161 and 163 ofsubstantially rigid and substantially resilient materials, respectively,constructed and operative in accordance with an alternative preferredembodiment of the present invention. As shown in FIGS. 18E and 18F,femoral heads 160 and 162 may be provided with apertures 164 and 166respectively, which may, for example, provide a passageway for synovialfluid, nerves, blood vessels, ligaments, tissues, elongated forcetransmitting members or prosthetic controls. Fluid in apertures 164 and166 may enhance the damping of femoral heads 160 and 162 respectively.

[0163] It is appreciated that the embodiments of FIGS. 18A-18F may beused as hinge or joint elements in other applications where it isdesired to provide different rigidity or resiliency in differentdirections of motion.

[0164] Reference is now made to FIG. 18C which illustrates an artificialacetabulum 400, constructed and operative in accordance with a preferredembodiment of the present invention.

[0165] Artificial acetabulum 400 preferably includes an interface 402made of a resilient, cartilage-like material, and preferably has agenerally triangular cutout 404. Acetabulum 400 preferably also includesan outer ridge 406 that “snap-fits” into the natural acetabulum socket,thereby substantially fixing artificial acetabulum 400 in the naturalsocket. The natural acetabulum may have to be drilled, cut or otherwisemachined to ensure a proper snap fit so that acetabulum 400 is rigidlyheld in place. Ridge 406 may be continuous or may be formed of discreteportions that protrude into the natural acetabulum recesses. As seen inFIG. 18G, interface 402 may comprise a deformable, resilient flange 408with expandable, accordion-like folds. Interface 402 may be one highlydeformable piece, or may be slightly deformable, in which case it mayfit into the natural acetabulum with a slight “click”.

[0166] It is a particular feature of the present invention that ridge406 provides shock absorption and positively locks interface 402 into arecess prepared in the natural socket, without any need for screws oradhesive. Interface 402 may comprise one or more layers. The largesurface area of interface 402 provides a large load bearing and shockabsorbing surface for a femoral head. Interface 402 may itself serve asan articulating surface for a femoral head, in which case the largesurface area diminishes fretting and wearing of the articulatingsurfaces.

[0167] Reference is now made to FIGS. 18K and 18L which illustrate across section of interface 402 constructed in accordance with twopreferred embodiments of the present invention. In FIG. 18K, it is seenthat interface 402 preferably includes a plurality of protrusions 410for locking interface 402 in recesses prepared in the natural socket. Asseen in FIGS. 18G and 18L, interface 402 may also include an “umbilical”protrusion 412 that is configured to fit the natural or restructured“umbilical” recess of the natural acetabulum. This allows reduction ofmachining of the innominate bone and leaves a stronger bone.

[0168] Acetabulum 400 also preferably includes a locking piece 414complementary shaped and sized to snugly fit into triangular cut-out404. Interface 402 together with locking piece 414 may be used as thearticulating portion of the prosthesis with the femur. Additionally,there is preferably provided an articulation portion 416 which snapstogether with a recess 418 formed in interface 402. Articulation portion416 may be made of metal, composite material, cartilage-like material,polyurethane or DYNEEMA. Articulation portion 416 may alternatively beattached to interface 402 by means of a bayonet type of connection orsimply a press fit without clicking. Articulating portion 416 makesartificial acetabulum 400 into one stable integral assembly which iseasily assembled in and removed from the innominate bone.

[0169] Reference is now made to FIGS. 18H, 18I and 18J which illustrateinstalling artificial acetabulum 400 into a natural acetabulum, inaccordance with a preferred embodiment of the present invention. In FIG.18H, an insertion tool 420 squeezes triangular cut-out 404 inwardly inthe direction of arrows 422, to allow insertion of interface 402 intothe natural socket. Upon release of insertion tool 420, cut-out 404springs outwards much in the manner of a retaining ring, therebypressing interface 402 firmly against and into the natural socket.Prongs of the insertion tool may be placed in prepared recesses or holesin interface 402.

[0170] In FIG. 18I, locking piece 414 is inserted into cut-out 404,thereby completing the shape of acetabulum 400 and firmly lockinginterface 402 into the natural socket when an articulating head or anadditional articulating surface is assembled therewith. In FIG. 18J,articulation portion 416 is snapped together with interface 402, therebymaking artificial acetabulum 400 into one integral assembly.

[0171] As mentioned above, the ligaments connecting the femur and theinnominate bone may be removed in the prior art, before placement of ahip joint prosthesis. Methods for preserving the hip joint ligaments, orreinforcing or replacing them, are now described.

[0172] Reference is now made to FIGS. 19A-19C which illustrate a methodof incision of ligaments, such as prior to insertion of a hip jointprosthesis, in accordance with a preferred embodiment of the presentinvention. A primary goal of the method of incision is to preserve theligaments.

[0173]FIG. 19A illustrates a hip joint 170 prior to incision. As seen inFIG. 19B, a wave-like incision 172 may be made, such as with a laserdevice, in any or all of the ilio-femoral, pubo-femoral andischio-femoral ligaments. As seen in FIG. 19C, the cut ligaments allowample room for placement of a hip joint prosthesis (not shown).

[0174] As is known in the art, ligaments generally contract afterincision, impairing mending of the ligament tissue. The wave-like shapeof incision 172 permits slightly shifting the ligaments so that there issufficient contact or overlap of the ligaments even after contraction,thereby helping to promote stitching and mending of the ligament tissue.

[0175] Reference is now made to FIG. 20 which illustrates a sleeve 180for joining a femoral head 182 with the innominate bone, constructed andoperative in accordance with a preferred embodiment of the presentinvention. Sleeve 180 is preferably made of a high strength wovenfabric, such as DYNEEMA, polyethylene, nylon or polyurethane. Sleeve 180preferably comprises filaments with a high elasticity modulus in thelongitudinal direction of the ligaments, along an axis 184, and acircumferential stretching weave along an axis 186, generallyperpendicular to axis 184, as seen in FIG. 20.

[0176] Sleeve 180 also preferably includes an anchoring band 188 forattaching sleeve 180 to the innominate bone. Anchoring band 188 may beattached to the innominate bone and sleeve 180 may be attached to thefemoral head by any suitable means, such as bonding or with mechanicalfasteners. Sleeve 180 may replace or assist the natural ligaments of thehip joint. Sleeve 180 may also help in mending of ligament tissue aftersurgery. All or portions of sleeve 180 may be constructed of a material,such as material used for dissolving sutures, which eventually dissolvesafter a predetermined period.

[0177] The present invention also provides a hip joint prosthesis whichmay substantially reduce the need for tampering with the hip jointligaments. Reference is now made to FIG. 21 which illustrates anexpandable artificial femoral head 190, constructed and operative inaccordance with a preferred embodiment of the present invention. Femoralhead 190 is preferably constructed of a resilient material, such aspolyurethane. When expanded, femoral head 190 has substantially the sameshape as femoral head 12, described hereinabove with reference to FIGS.2 and 3.

[0178] In contrast to the prior art, femoral head 190, before expansion,may be inserted between the existing ligaments with minimum tamperingthereof. Femoral head 190 may then be expanded to the desired shape.Femoral head 190 may be inflated by means of a fluid (not shown)introduced, for example, via a thin needle valve (not shown).Alternatively, femoral head 190 may be expanded by introducing thereincomponents of an expandable foam (not shown), which expand insidefemoral head 190.

[0179] The present invention will now be described in detail withrespect to a prosthesis for a ginglymus, namely the knee joint. For abetter understanding of a knee joint prosthesis, a basic description ofthe human knee joint is presented here with reference to FIG. 22, whichillustrates the knee of the right leg.

[0180] The knee is a hinge comprising the internal and external condylesof the femur which articulate with the upper end of the tibia. Thefemoral condyles are separated by a deep fossa. The upper end of thetibia comprises two tuberosities, the external of which articulates withthe head of the fibula.

[0181] The knee also comprises the trochlea of the femur (not shown inFIG. 22) which is located forward and upward of the condyles. Thepatella slides along the trochlea. The patella is shown pulled down inFIG. 22 in order to show some of the ligaments and cartilage whichconnect the femur, tibia, fibula and patella. These ligaments andcartilage include, inter alia, the external lateral ligament whichconnects the external femoral condyle to the fibula, the internallateral ligament which connects the internal femoral condyle to thetibia, the ligamentum patellae to which is attached the patella, and thetransverse ligament and internal semilunar cartilage which are attachedto the head of the tibia. The transverse ligament, internal semilunarcartilage and the anterior crucial ligament are attached to the spine(not shown in FIG. 22) of the tibia. The spine is a series of elevationson the head of the tibia opposite the fossa between the femoralcondyles.

[0182] Reference is now made to FIGS. 23 and 24 which illustrate a kneeprosthesis 200, constructed and operative in accordance with a preferredembodiment of the present invention. Knee prosthesis 200 comprises anupper or femoral portion 202 and a lower or tibial portion 204, as seenin FIGS. 23 and 24.

[0183] Referring additionally to FIG. 25, it is seen that femoralportion 202 preferably comprises two pads 206 upon which rest theinternal and external condyles of the femur, as seen in FIG. 24, and atrochlear portion 208 which is intermediate the patella and thetrochlea, as seen in FIG. 23. Pads 206 articulate with tibial portion204. As seen in FIG. 25, femoral portion 202 also preferably has asocket 210, whose function is described hereinbelow with reference totibial portion 204.

[0184] Referring additionally to FIG. 26, it is seen that tibial portion204 includes an artificial spine 212 which extends into socket 210. Itis appreciated that when the knee flexes, socket 210 restricts themovement of spine 212 therein. Socket 210 and/or spine 212 arepreferably constructed of a shock absorbing or resilient material, suchthat the movement of spine 212 is cushioned at the limits of travel insocket 210.

[0185] As seen in FIG. 23, spine 212 may extend beyond socket 210 intothe fossa of the femur. Tibial portion 204 also preferably has twodepressions 214 with which pads 206 may articulate. Tibial portion 204preferably includes a stem 216 for attachment to the tibia. Tibialportion 204 may have one or more hollow portions 218 to increase shockabsorption, damping or resiliency.

[0186] As seen in FIG. 23, a tibial cushion 220 may be placedintermediate tibial portion 204 and the head of the tibia, tibialcushion 220 preferably being constructed of a material compatible withhuman tissue, such as polyurethane. In accordance with a preferredembodiment of the present invention, femoral portion 202 may beconstructed of a substantially rigid material, such as a compositematerial, and tibial portion 204 may be constructed of a substantiallyresilient material, such as polyurethane.

[0187] In accordance with another preferred embodiment of the presentinvention, femoral portion 202 may be constructed of a substantiallyresilient material and tibial portion 204 may be constructed of asubstantially rigid material.

[0188] In accordance with yet another preferred embodiment of thepresent invention, femoral portion 202 may be constructed of asubstantially resilient material and tibial portion 204 may beconstructed of a substantially resilient material.

[0189] It is appreciated that knee prosthesis 200 is operative to absorbstatic and dynamic shocks.

[0190] It is a particular feature of the present invention that theresiliency of either femoral portion 202 or tibial portion 204 allowsthe configuration of the contact surfaces between portions 202 and 204to change according to physical factors, such as load or motion. Forexample, when bearing loads directed downwards on the tibia, the contactarea between portions 202 and 204 becomes relatively large, therebyincreasing stability and decreasing pressure on the tibia. When the kneeflexes, the contact area is relatively small, which facilitates motionof the tibia with respect to the femur. Femoral portion 202 and tibialportion 204 have different radii of curvature when not exposed toforces. The radii of curvature approach equality when bearing forcesdirected downwards on the tibia.

[0191] Reference is now made to FIGS. 27 and 28 which illustrate a kneeprosthesis 230, constructed and operative in accordance with anotherpreferred embodiment of the present invention. Knee prosthesis 230comprises an upper or femoral portion 232 and a lower or tibial portion234, as seen in FIGS. 27 and 28. Tibial portion 234 is substantiallyidentical to tibial portion 204 described hereinabove with reference toFIGS. 23, 24 and 26.

[0192] Femoral portion 232 preferably comprises two pads 236 upon whichrest the internal and external condyles of the femur, as seen in FIG.28, and a trochlear portion 238 which is intermediate the patella andthe trochlea, as seen in FIG. 27. Pads 236 articulate with tibialportion 234. Pads 236 preferably have one or more hollow portions 240,and may have one or more fluid passageways 242, for permitting flowtherethrough of synovial fluid, thereby providing lubrication andenhancing the shock absorbing and damping characteristics of kneeprosthesis 230.

[0193] Femoral portion 232 articulates with tibial portion 234 of kneeprosthesis 230 by sliding along the generally concave surface of tibialportion 234. Reference is now made to FIGS. 29 and 30 which illustrate aknee prosthesis 250, constructed and operative in accordance withanother preferred embodiment of the present invention. Knee prosthesis250 comprises an upper or femoral portion 252 and a lower or tibialportion 254, as seen in FIGS. 29 and 30. Femoral portion 252 ispreferably generally convex and articulates with tibial portion 254 byrolling along the generally convex surface of tibial portion 254.

[0194] As described hereinabove with reference to FIG. 23, theresiliency of either femoral portion 252 or tibial portion 254 allowsthe configuration of the contact surfaces between portions 252 and 254to change according to physical factors, such as load or motion.

[0195] Reference is now made to FIGS. 31 and 32 which illustrate a kneeprosthesis 260, constructed and operative in accordance with anotherpreferred embodiment of the present invention. Knee prosthesis 260comprises an upper or femoral portion 262 which articulates with a loweror tibial portion 264 by means of one or more roller elements 266, asseen in FIGS. 31 and 32.

[0196] Portions 262 and 264 may be substantially rigid and rollerelements 266 may be substantially resilient. Conversely, portions 262and 264 may be substantially resilient and roller elements 266 may besubstantially rigid.

[0197] Roller elements 266 may permit articulation of femoral portion262 with tibial portion 264 by means of rolling, sliding, a combinationof rolling and sliding, or rolling combined with a deformation of one ormore of roller elements 266. Roller elements 266 may be formed in anyshape which provides such rolling and sliding, such as being generallycylindrical in shape. An alternative shape is shown in FIG. 33.

[0198] At least one fluid passageway 268 may be provided in each rollerelement 266 for passage therethrough of a fluid, such as synovial fluid,thereby providing lubrication and enhancing the shock absorbing anddamping characteristics of knee joint prosthesis 260.

[0199] Alternatively or additionally, each roller element 266 may haveat least one hollow portion. Alternatively or additionally, each rollerelement 266 may comprise a plurality of portions, each portion notnecessarily having the same mechanical or physical properties. Theseportions may be used to enhance, to optimize or to customize the shockabsorbing and damping characteristics of the roller element 266.

[0200] Femoral portion 262 may be attached directly to the femoralcondyles. Alternatively, as shown in FIG. 32, a femoral pad 270 may beplaced intermediate femoral portion 262 and the femoral condyles.Femoral pad 270 may be constructed of a material with properties similarto human cartilage, such as polyurethane.

[0201] Reference is now made to FIG. 34 which illustrates a bonefastener 300 for fastening bone fractures, constructed and operative inaccordance with a preferred embodiment of the present invention.

[0202] Bone fastener 300 preferably includes a core 302 and an outerlayer 304. Outer layer 304 preferably includes one or more ridges 306,which, inter alia, help distribute stresses and help fasten bonefastener 300 to a bone. Core 302 may be of solid or hollow construction.Bone fastener 300 may have any suitable cross sectional shape, such ascircular or elliptical.

[0203] In accordance with a preferred embodiment of the presentinvention, core 302 is preferably constructed of a rigid material, forexample, stainless steel or a structural plastic. Alternatively, therigid material may be a composite material, such as graphite fibers,which may be constructed to have mechanical or physical properties, suchas modulus of elasticity or coefficient of thermal expansion, equivalentto that of the local human bone.

[0204] Outer layer 304 is preferably made of a resilient materialcompatible with human tissue, such as polyurethane, which helpsdistribute stresses optimally, thereby stimulating regeneration of bone.In accordance with a preferred embodiment of the present invention,outer layer 304 is constructed of a material, such as polyurethane,which has one or more mechanical and/or physical propertiessubstantially similar to human cartilage.

[0205] Reference is now made to FIG. 35 which illustrates a vertebrareplacement 310, constructed and operative in accordance with apreferred embodiment of the present invention.

[0206] Vertebra replacement 310 preferably includes at least one innermember 312, at least one intermediate member 314 and at least one outermember 316. Inner member 312 is preferably constructed of asubstantially resilient material and may have one or more hollowportions 318. Alternatively, portions 318 may be filled with a fluid,such as synovial fluid. Additionally or alternatively, a fluidpassageway (not shown) may be provided for fluid flow therethrough,thereby providing lubrication and enhancing the shock absorbing anddamping characteristics of vertebra replacement 310.

[0207] Intermediate portion 314 may be less flexible than inner member312, and is preferably constructed of a rigid material, for example,stainless steel or a structural plastic. Alternatively, the rigidmaterial may be a composite material, such as graphite fibers, which maybe constructed to have mechanical or physical properties, such asmodulus of elasticity or coefficient of thermal expansion, equivalent tothat of the local human bone.

[0208] Outer members 314 are preferably made of a resilient materialcompatible with human tissue, such as polyurethane, which helpsdistribute stresses optimally. In accordance with a preferred embodimentof the present invention, outer members 314 may be constructed of amaterial, such as polyurethane, which has one or more mechanical and/orphysical properties substantially similar to human cartilage.

[0209] In accordance with a preferred embodiment of the presentinvention, geometrical data may be provided, such as by computerizedtomography, and be used to prepare and select an optimal prosthesis orbone fastener prior to surgery. Data input, such as from the results ofcomputerized tomography, may be used to match the geometry of theprosthesis or bone fastener to the needs of the patient. Either theprosthesis or the bone, or both, may be shaped, such as by computerizedmachining, using the geometrical data obtained.

[0210] Alternatively, the geometry of a preformed, standard prosthesismay be used to reshape the bone to match the prosthesis. Alternatively,the geometrical data used to reshape the bone may be used generally toform the prosthesis in real time.

[0211] It is appreciated that various features of the invention whichare, for clarity, described in the contexts of separate embodiments mayalso be provided in combination in a single embodiment. Conversely,various features of the invention which are, for brevity, described inthe context of a single embodiment may also be provided separately or inany suitable subcombination.

[0212] It will be appreciated by persons skilled in the art that thepresent invention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present invention isdefined only by the claims that follow:

1. A hip joint prosthesis comprising an artificial femoral head which isadapted to articulate with both a femur and an acetabulum.
 2. A hipjoint prosthesis according to claim 1 and wherein said artificialfemoral head is constructed of a relatively rigid material, compatiblewith human tissue.
 3. A hip joint prosthesis according to claim 1 andwherein said artificial femoral head is constructed of a material whichis shock absorbing.
 4. A hip joint prosthesis according to claim 1 andwherein said artificial femoral head is constructed of a material whichis resilient.
 5. A hip joint prosthesis according to claim 1 and whereinsaid artificial femoral head is generally spherical.
 6. A hip jointprosthesis according to claim 1 and wherein said artificial femoral headis formed with a hollow core.
 7. A hip joint prosthesis according toclaim 1 and also comprising an artificial acetabulum having anarticulating surface with which said artificial femoral headarticulates.
 8. A hip joint prosthesis according to claim 1 and alsocomprising an artificial femoral socket having an articulating surfacewith which said artificial femoral head articulates, said artificialfemoral socket being adapted for fixed attachment to said femur.
 9. Ahip joint prosthesis according to claim 2 and also comprising anartificial femoral socket having an articulating surface with which saidartificial femoral head articulates, said artificial femoral socketbeing adapted for fixed attachment to said femur.
 10. A hip jointprosthesis according to claim 1 and wherein said artificial femoral headis formed with fluid passages adapted to allow flow therethrough ofsynovial fluid.
 11. A joint prosthesis comprising an artificial ballelement which is adapted to articulate with both first and second ballsockets defined by a joint.
 12. A joint prosthesis according to claim 11and wherein said artificial ball element is constructed of a relativelyrigid material, compatible with human tissue.
 13. A joint prosthesisaccording to claim 11 and wherein said artificial ball element isconstructed of a material which is shock absorbing.
 14. A jointprosthesis according to claim 11 and wherein said artificial ballelement is constructed of a material which is resilient.
 15. A jointprosthesis according to claim 11 and wherein said artificial ballelement is generally spherical.
 16. A joint prosthesis according toclaim 11 and wherein said artificial ball element is formed with ahollow core.
 17. A joint prosthesis according to claim 11 and alsocomprising an artificial ball socket having an articulating surface withwhich said artificial ball element articulates.
 18. A joint prosthesisaccording to claim 11 and also comprising an artificial ball elementsocket having an articulating surface with which said artificial ballelement articulates, said artificial ball element socket being adaptedfor fixed attachment to a bone.
 19. A joint prosthesis according toclaim 12 and also comprising an artificial ball element socket having anarticulating surface with which said artificial ball elementarticulates, said artificial ball socket being adapted for fixedattachment to a bone.
 20. A joint prosthesis according to claim II andwherein said artificial ball element is formed with fluid passagesadapted to allow flow therethrough of synovial fluid.